This disclosure relates generally to flyback converter-based power converters that are capable of providing multiple output voltage levels in an efficient manner. Other embodiments are also described herein.
Alternating current (AC) power is typically supplied from wall outlets and is sometimes referred to as line power. Electronic devices often include circuitry that runs from direct current (DC) power. AC to DC power converter circuitry can be used to convert AC power to DC power. The DC power may be used to power an electronic device that runs on DC power. The DC power may also be used to charge a battery in an electronic device.
AC to DC power converters often include transformers. A transformer in an AC to DC power converter may have primary and secondary windings. A pulse width modulation (PWM) circuit on the primary side of a transformer may generate pulses of current that pass through the primary winding of the transformer. On the secondary side of the transformer, a diode may be used to rectify the output of the secondary winding.
Some AC to DC power converter circuits use synchronous rectifier (SR) output stages. SR output stages may include a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET is driven so as to rectify the output waveform from the transformer in the same way that the diode is used in other power converter designs, while avoiding high diode voltage drops when conducting current (e.g., ˜0.7V).
Certain power converter designs may have potential drawbacks. One drawback is that different electronic devices may have different voltage requirements. Bias circuits that supply bias voltages are designed at a particular operating voltage. Efficient operation at one level may result in inefficient operation at another level since the topology of the bias circuit cannot change.
To attempt to deal with some of these drawbacks, some power converters may use bias circuits to control primary side and secondary side circuits. These bias circuits use voltages from one or more auxiliary transformer windings to generate control voltages to the primary and secondary side circuits. However, such configurations can result in inefficient operation in power converters that produce multiple outputvoltages.